This invention concerns substance releasing materials which may provide phased release of said substance over a period of time. The invention relates particularly, though by no means exclusively, to product packaging materials which release a substance for purposes beneficial to the product contained therein, and to mulches for agricultural and horticultural use.
Regarding the latter application, techniques have been developed recently to enhance plant growth by covering the soil with a mulch. A mulch can be any suitable product such as fibrous materials (eg cotton waste or wood chippings), paper or board of plastic sheeting (film).
The concept is to improve the growth of the desirable plant (crop) due to improved soil warming, improved germination, undesirable plant growth suppression (weeds), improved soil moisture retention, either by each individual factor, or in any combination. Lately, the use of plastic film has grown, and in particular by modifying the structure of the film, several of the above desirable features have been developed. This can include such items as infra-red retention (soil warming), varying biodegradability films to suit the plants growth season and by degrading rendering the plastic harmless, or conversely non-degradable so that it may be re-used.
Any weed suppression benefits from a mulch, are due to barrier effects, either mechanical or light whereby the weed cannot xe2x80x9cseexe2x80x9d the light and hence cannot photosynthesise. These types of mulches are usually wood or bark chippings and are used in parks and recreation grounds to lower weeding costs. They are expensive to apply and, since they are slow to rot, they are not suitable for agricultural applications.
As seen in the large scale applications, film is used in cash value crops such as early potatoes, lettuce, leeks and cut flowers. This enables the grower to benefit from earlier maturation, and thus gain from higher early to market prices. Higher yields are also a frequent bonus. Two techniques are used. The first is to sow the crop, usually in beds, and then the plastic is laid over the bed in a strip and a small amount of soil is ploughed back over the edges to prevent the wind from lifting the sheet and blowing it away. Once the crop germinates and shows sufficient growth above the soil surface, the film is removed, since it cannot break through the plastic. In this instant, non-degradable film is used.
The second method uses degradable film which remains on the soil. The seed is drilled through the plastic by piercing it, and the plant then grows through it. Depending upon the composition of the film, it degrades and after harvest any remains are ploughed into the soil. The degradation mechanism is normally activated by moisture, but ultra-violet light types can also be used.
There are two major problems with using mulches in this manner. The first is that the beneficial growing environment for the crop is also good for stimulating weed growth. Control of this undesirable side effect is by use of pre-emergence sprays whereby the land is sprayed before the crop is sown. This in its turn has problems since the grower has to guess what weeds will become a problem, and thus the type of spray to use, as well as the added costs involved with this operation, which in any case may not be necessary. In addition, the use of such sprays is not always very effective, and there is the additional problem of added pollution.
The second problem is that it is not possible to travel over the land after application of the mulch since this will damage the film. Any subsequent applications of pesticides and/or fungicides are not possible except by the expensive use of aircraft, and the film itself prevents the absorption into the soil (and then into the plant) of herbicides or later applications of fertiliser.
Once the crop is sufficiently established and damage to the film no longer matters, sprayers can travel over the land. This in turn means that the grower""s natural tendency is to overuse sprays as a preventative measure, thus leading to pollution problems. The spray is spread universally, over what will become food with the possibility of as yet unknown health problems. Dosage rates have to be carefully administered to ensure effectiveness without crop damage, since it is not possible to direct the spray away from the crop.
It is another object of the present invention to provide product packaging materials which permit the phased release of a substance, or substances, beneficial to the product.
According to the invention, there is provided a substance releasing material comprising a substrate having at least one beneficial substance adhered thereto by at least one layer of bonding agent, in which phased release of the beneficial substance or substances is effected by the action of a release agent on the bonding agent.
The substance or substances may be coated onto the substrate and overlaid with the bonding agent.
The substance or substances may be contained within the layer or layers of bonding agent.
The substance material may comprise multiple layers of bonding agent and beneficial substance or substances.
According to one aspect of the invention, the substrate comprises packaging for a product, and the release of the substance is beneficial to the product.
The packaging may comprise plastic, paper, cardboard or a woven material.
The packaging may comprise an insert.
The substrate may have one layer of bonding agent including the substance or, alternatively, the layer may include a plurality of substances.
The substrate may have a plurality of layers of bonding agent.
The bonding agent may be a lacquer.
The release agent may permeate the substrate prior to acting upon the bonding agent, in which instance the release agent may be atmospheric oxygen, carbon dioxide or water.
The release agent may be introduced into the package comprising the product and the packaging.
The release agent may be contained in the product itself.
The release agent may be heat.
The substance may comprise an anti-rust agent.
The substance may comprise a foodstuff preservative, which may be an anti-oxidant or an essential oil.
The substance may comprise a sterilising agent.
The substance may comprise a foodstuff flavouring.
The layer, or layers may be coated onto the substrate, and the coating may be performed using a printing technique. Designs or text may be simultaneously printed onto the substrate.
According to another aspect of the invention, there is provided a mulch comprising a sheet substrate which has been coated with one or more substances beneficial to crop growth and overcoated with at least one layer of bonding agent. Examples of substances beneficial to crop growth are fertilisers, insecticides, pesticides, fungicides, nematicides and herbicides.
The substance or substances may be print coated. The bonding agent may be a lacquer.
The sheet may be of plastics, paper or textile fabric.
The sheet may be impervious or perforated to allow moisture to pass therethrough.
The sheet may be transparent or coloured.
The density of the coating of different substances may vary across the width of the sheet.
Fertilisers, insecticides, pesticides, fungicides or nematicides, or combinations thereof may be concentrated on areas of the sheet which will overlay the crop.
Herbicides may be concentrated on areas of the sheet which will overlay the spaces between adjacent rows of crop.
Seed may be adhered to the mulch before it is laid.
The bonding agent may be printed at a central facility or at an on site mobile facility at the time it is laid.